Digital compact disks were originally conceived in the early 1980's as a technique to accurately copy and preserve audio recordings intended for sale to a mass market of consumers. As computing power has increased exponentially since that time, information processing tasks unthinkable only a few years ago have become commonplace and require large amounts of data most economically and conveniently stored on digital compact disks.
Until recently the transfer of data onto compact digital disks was a costly procedure economically feasible only when manufacturing a large quantity of copies. Users whose applications required relatively few copies or required frequent data updates could not reap the benefits of this technology, even though low-cost disk-readers were readily available.
The advent of recordable digital compact disks, generally referred to as "CD-R" disks, was intended to allow users to record their own disks and thereby achieve significant savings. Unlike a common compact disk that has been pressed by a mold, a CD-R has a dye layer that is etched by a laser contained in the CD-R disk drive. Once etched, the "burned" CD-R disk is unalterable and will retain data for approximately 75 years.
Several practical problems have prevented CD-R users from attaining maximal efficiency in the copy process, especially when attempting to make multiple disk copies in a short amount of time. The primary problem occurring in this situation is that the data throughput from the data source, such as a file on a hard disk drive or a master compact digital disk, to the write head of the CD-R drive is interrupted during the copy process. Many times when this occurs the data buffer to the write head of the CD-R drive is exhausted and null data is written onto the CD-R disk, making the CD-R disk irrevocably defective.
The frequency of such a defective CD-R disk write increases at least linearly as the drive speed of the CD-R writing head is increased. The industry standard speed is approximately 150K Bytes per second. Some CD-R disk drives can write data at four times this standard speed, but while this increased speed lowers the total copying time, the frequency of defective CD-R disk writes increases as data throughput from the data source is increased.
An additional problem in a volume copying process is the necessity for direct human supervision to prepare CD-R disks for copying, remove the disks from the CD-R disk writer once copying is complete, and then prepare the disks for inspection to ensure no defective CD-R disks are retained in the completed set of copies. Aside from the tedium involved that may indirectly add errors, requiring human attention in this process adds a significant labor cost that is added to the end-user price.
The copy speed versus accuracy problem described above is solved when the CD-R disk writer is configured to concurrently copy the data onto multiple CD-R disks. For example, the total copy time for two CD-R disk drives concurrently copying data at 150K Bytes per second is the same as one CD-R disk drive serially copying two CD-R disks at 300K Bytes per second, and the frequency of disk write errors using the concurrent disk drives is approximately half that of the serial disk drive.
This system uses the concurrent copying method described above and also eliminates the necessity of direct human supervision of the copy process through the unique circular arrangement of CD-R disk spindle members around a pivotal transport tower containing a disk,pickup head that lifts a blank disk from a disk spindle member and transports the disk to one of the available stacked CD-R disk drives. After the recording process is complete the disk pickup head retrieves and transports the burned CD-R disk copy to a specified disk spindle member for copied disks.
The electrical and physical configuration of this system provides several additional benefits to users. The semi-circular arrangement of disk spindle members around the pivotal transport tower minimizes the number of moving parts needed to construct the disk transport assembly. A system having more disk spindle members can be constructed by increasing the radius of the circle formed by the disk spindle members. Similarly, the arrangement of two stacked sets of recordable disk drives allows for a scaleable design permitting the user to make low-cost upgrades.
Prior disk copy methods only provided for lineal copying of a single source disk. The configuration of this system allows for several master compact disks to be transportable by the disk hub to a selected disk read head so that the copy process from the master compact disks is a random access process.
Yet another benefit provided by this system is the system's ability to test burned CD-R disks for disk write errors, and through use of the pivotal transport tower, eject a defective CD-R disk isolating the defective CD-R disks from the set of properly burned CD-R disks.